High performance radio frequency (RF) circuits are utilized in communication equipment, sensing equipment, and other RF circuits. Generally, such circuits often utilize band pass filters. The band pass filters can be employed as intermediate frequency (IF) filters used in RF circuits. Multi-band digital radios often utilize multi-chip module receivers and exciters that require band pass filters. Such multi-band digital radios can be utilized in joint tactical radio systems (JTRS).
According to one particular application, conventional multi-band digital intermediate frequency (IF) radio systems require two to three programmable RF translations to establish the received signal in a fixed frequency (pre analog-to-digital conversion (ADC)) with minimal in band distortion. On the receive side of the radio, the signal is often received by at least one IF analog filter with minimal in bandwidth distortion before analog-to-digital conversion (ADC). On the transmit side of the radio, the signal is often transmitted through an IF analog filter after digital-to-analog conversion (DAC).
Multi-band and multi-signal-type operation of radio systems generally require quality programmable IF filters. Quality programmable IF filters should be highly integratible into single multi-chip module receivers and exciters, should be highly linear with low noise figure, should have accurate tuning control including temperature and tolerance factors, and should have step programmable bandwidth control with a robust shape factor. Such high quality programmable IF filters are typically too expensive and require excessive size and weight. Heretofore, the size and cost of the RF and IF translations is relatively large for highly integrated multi-chip-module receivers and exciters. The size and cost is often due, at least in part, to the size and cost of the band pass filters required for IF band pass filtering.
Therefore, there is a need for a method of filtering that is programmable in bandwidth and/or frequency and is highly integratible in IC technology. Further, there is a need for a method of achieving a programmable IF filter that can reduce the number of RF translations required (preferably to one). Further, there is a need for a programmable IF filter that can reduce RF communication circuitry, sensing circuitry, or other equipment size and cost. Further still, there is a need for a programmable IF filter that can be combined with a variable data converter clock rate to reduce radio size and cost. Further, there is a need for a programmable IF sampling band pass filter that has at least one or more of the following characteristics: 1) it is highly linear with low noise figure potential, 2) it is coherently sample rate matched to the data converter, 3) it has a programmable sample clock rate that provides accurate frequency control that has symmetrical (about the center frequency) programmable bandwidth step control and has constant Q with respect to frequency, 4) it has a cascadable configuration for performance flexibility, 5) it supports harmonically sampled single translation options, 6) it has data converter performance enhancement potential, and 7) it is highly integratible into single MCM receivers and exciters. Yet further, there is a need for a programmable IF filter combined with a variable data converter clock rate for reducing the size and cost of virtually any radio architecture.